CUMULATIVE EFFECTS OF OPTIMUM AND 

 SUBOPTIMUM TEMPERATURES ON 

 INSECT DEVELOPMENT^ 



A. Glenn Richards, Department of Entomology and Economic 

 Zoology, University of Minnesota, St. Paul, Minnesota 



HE VOLUMINOUS LITERATURE on the effects of temperature on develop- 

 ment in general or on insect development in particular leaves numerous 

 questions unanswered (1-3, 9». The present paper will deal with two of 

 these questions, namely, why is the hatching threshold several degrees 

 above the temperature at which the developmental rate approaches zero; 

 and why are insects which hatch under near minimal conditions so de- 

 bilitated that they subsequently die even though placed under optimal 

 conditions? 



As experimental material for this study a laboratory colony of the 

 Large Milkweed Bug, Oncopeltus fasciatus (Dallas) (Order Hemiptera), 

 was used. This species gives the type of growth curves commonly obtained 

 from insects (8). The time-temperature curve for hatching (fig. 1, curve 

 A) is nearly a hyperbola but discrepancies from the hyperbolic form are 

 well shown by the reciprocal, the rate-temperature curve (fig. 1, curve B), 

 which is clearly not a straight line. Various attempts have been made to 

 find an algebraic expression satisfying these curves. Thus, Browning (4) 

 finds closer fit with a logistic curve and HufTaker (6), with a catenary 

 curve. It does not seem worthwhile to discuss the application of these 

 various equations since there is no sound basis for thinking any one of 

 them gives a portrayal of relevant phenomena. Their appearance in the 

 literature seems to be no more than the outcome of an empirical search 

 for a mathematical model that will produce a curve of this shape, and any 

 correspondence found might be fortuitous. 



However, it should be said that the search for a satisfactory equation 

 has a practical basis which makes fortuitousness of fit immaterial. It 

 would be exteremely useful, especially for ecological work in the field, to 

 have an equation by means of which one could calculate the hatching 

 threshold from a few points without the laborious laboratory work in- 

 volved in empirical determination of this threshold. Unfortunately, like 

 previous investigators, we have not found it possible to approximate this 



^ Paper No. 3615, Scientific Journal Series, Minnesota Agricultinal Experiment 

 Station, St. Paul 1, Minn. 



145 



